The main bearing members for loads placed on flatbed trailers are the pair of I-beams, generally known as the "main beams" which run longitudinally the length of the bed. Properly fabricated, the beams are flexed or curved vertically upward and designed to compress or straighten longitudinally under load. Floor supports in the form of a multiplicity of "C" channel, or "I-beam", cross members are bolted or welded perpendicularly to the webs of the main beams and directed outboard to define the width of the bed. Disposed on top of the cross members are floor sections, typically welded to each other longitudinally or butted against each other snugly and held in position by guide structures and floor screws.
Two basic problems occur in these constructions. Welding of the cross members and floor sections to the main beam reduces its load bearing strength most particularly if it is heat-treated aluminum and therefore requires a sacrifice in load capacity by as much as 20%. In the butted floor section construction, since the floor sections are essentially loose, they serve very little load bearing function and do not compress with the main beam. What they do is transmit the load to the underlying cross member which, in turn, transmits the load to the main beam. Furthermore, the typically preferred use of aluminum in flatbed trailer construction to increase load capacity is particularly defeated by extensive welding and loose floor sections tend to minimize payload.
The following U.S. patents are related to the field of truck construction.
Various types of truck body construction are disclosed in U.S. Pat. Nos. 1,962,497 (Francis); 2,818,272 (DeLay); 3,003,810 (Kloote et al.); 3,096,996 (Cole); 3,163,434 (Krueger); 3,393,920 (Ehrlich); 3,692,349 (Ehrlich); 3,843,156 (Alfriend, Jr. et al.); 4,221,427 (Sentle, Jr. et al.); 4,232,884 (DeWitt); 4,671,562 (Broadbent); 4,787,669 (Wante); 4,906,021 (Rowe et al.); 5,085,025 (Gaddis); 5,188,418 (Walworth, Jr. et al.); 5,205,587 (Orr); 5,401,050 (Baker); 5,417,453 (VanDenberg); 5,474,331 (Booher); 5,558,369 (Cornea et al.); and 5,655,792 (Booher).
Various floor constructions for trucks are disclosed in U.S. Pat. Nos. 2,485,047 (Greig); 2,773,718 (Bohlen); 4,656,809 (Wilson); 4,951,992 (Hockney); 5,054,843 (Gray).
Conventional prior art truck bed designs are depicted in FIGS. 1-3. In particular, FIG. 3 shows the typical two main rail "I-beam" 10 design whereby the main rails 10 run the length of the truck bed and are designed for supporting the payload. Each I-beam 10 comprises an upper flange 11, a lower flange 13 and a web 15. Cross members 12 are transversely coupled between the main rails 10 through the webs 15. It should be understood that U-shaped cross members 12 are depicted for example only; other conventional types of cross members could have been depicted such as I-beam, c-channel or circular cross-sectioned cross members. Flooring members 14 are then disposed in between the main rails 10 on top of the cross members 12; these flooring members 14 may have feet 16 (FIGS. 1 and 3) or even a bottom surface 18 (FIG. 2) that rest on top of the cross members 12. These feet 16 or bottom surface 18 can then be fastened to the cross members 12 by bolting or welding (not shown). In these instances, the top surface 20 of the flooring member 14, where the payload is eventually positioned, is thus set off from the top surface 22 of the cross member 12.
However, in such a design the three main components, i.e., the main rails 10, the cross members 12 and the flooring member 14, all work independently of each other. Such a design does not efficiently transfer the load from the payload into the main rails 10. When the payload is positioned on the flooring members 14 for transport, the weight is transferred through the top surface 20 of the flooring member 14, through the feet 16 and bottom surface 18 (if present), through the cross members 12 and eventually to the main rails 10. In contradistinction, the optimum design would have the payload resting directly on the main rails 10, i.e., unitizing of the top surface of the flooring member 14 with the top surface of the cross members 12 and the main rails 10.
Thus, there remains a need for a lightweight, integrated flatbed design that effectively makes the top surface of the floor the top surface of the main rails and the top surface of the cross members, thereby allowing the direct transfer of load from the payload to the main rails.